Ion implantation is a process that alters the physical, chemical, or electrical properties of a material and is used in a wide range of commercial and industrial applications. In general terms, an ion implanter generates an ion beam, accelerates the ion beam in an electrical field, and impacts the ion beam into a solid material. Ion implantation is used extensively in the fabrication of semiconductors, where doped regions such as sources and drains are formed in semiconductor substrates by implanting ion impurities.
One of the components of an ion implanter is the ion source, which generates the ion beam. An ion source forms an ion beam by admitting a small amount of gas into an arc chamber's reaction cavity, where a heated cathode emits electrons causing ionization of the gas and the formation of a plasma in the reaction cavity. The positively-charged ions are then drawn from the arc chamber using a negatively-charged anti-cathode positioned near a small opening in the arc chamber through which the ion beam exits.
There are two types of widely-used ion sources: directly heated cathodes, having a cathode for emitting electrons—usually a single-turn helical filament—mounted openly in the reaction cavity, and indirectly heated cathodes, having a cathode heated by electron bombardment from a filament causing thermionic emission of electrons from the cathode into the reaction cavity.